APPENDIX D1.1: Preliminary Design Report - zitholele - BA for 3 Canals/3. Final Basic... · APPENDIX D1.1: Preliminary Design Report. ... summarised in the table below. ... 6.1 Basis

ZITHOLELE CONSULTING

APPENDIX D1.1: Preliminary Design Report

Zitholele Consulting (Pty) Ltd

PO Box 6002 Halfway House 1685 South Africa Thandanani Park, Matuka Close Halfway Gardens, Midrand Tel + (27) 11 207 2060 Fax + (27) 86 674 6121 E-mail : [email protected]

DESIGN OF THREE CANALS IN THE WITWATERSRAND MINING BASIN

PRELIMINARY DESIGN REPORT

REPORT NO. 12792-Rep-002 Rev 01

Submitted to:

COUNCIL FOR GEOSCIENCE Silverton Pretoria

0184

APRIL 2013


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EXECUTIVE SUMMARY

The Department of Mineral Resources (through the Council for Geoscience) intends implementing measures for

the prevention of water ingress into mined out areas in the Witwatersrand Goldfields. Three canals have been

identified, within natural watercourses, for lining along and across streams traversing shallow undermined areas

in the Witwatersrand Goldfields.

The canals identified under this project are:

Durban Roodepoort Deep(DRD) West Rand 2,400 metre section

New Canada Dam (NCD) Central 600 metre section

Elburgsrpuit (ELB) East Rand 590 metre section

The Inception stage is complete and was captured in the Project Implementation Report. The Project

Implementation Plan was approved by CGS before commencing with the Concept and Viability Phase. This

report documents what has been undertaken during the Concept and Viability Phase.

As a precursor to the Concept and Viability Stage, a topographical survey and geotechnical investigation was

initiated. It was also deemed necessary to confirm the areas of water ingress by undertaking a desktop study as

well as site measurements. The geotechnical investigation and topographical surveys are complete.

The Guideline for Human Settlement dictates that a 5 year recurrence interval storm event should be used to

determine the canal size. However, it was agreed that the 2 year storm event will also be modelled. Hydrosim, a

kinematic stormwater model, was used to determine the flows and size the canals. The results of this exercise is

summarised in the table below. Illegal discharge is not considered.


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Site Recurrence

Interval

Flow (m3/s) Design height

(mm)

Required

Height (mm)

Velocity (m/s)

DRD

2 94 1,560 3.89

5 144 2,000 4.37

NCD

2 81 1,550 3.22

5 120 2,000 3.31

ELB

2 81 1,523 4.78

5 118 1,900 4.89

The HEC-RAS backwater model was used to determine the adequacy of the existing culverts at each of the sites

to convey the 2 and 5 year storm events. The culverts at NCD proved adequate for both the storm events. At

the DRD site, the existing culvert could not manage the 5 year storm event without having a significant back

water effect. Both the 2 and 5 year storm events could not be conveyed via the culverts located at the

Elbursgpruit site. Once the design period is confirmed, these culverts will be designed accordingly.

A matrix, with the possible alternatives, was undertaken to determine the feasible options for canal lining to take

forward. Of the possible alternatives, the concrete and reno-mattress lining were taken forward and priced. The

cost estimate, along with the unit cost estimate, is summarised in the table below.


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Reno-mattress (cost in Rands) Concrete liner (cost in Rands)

2 Year Storm 5 Year Storm 2 Year Storm 5 Year Storm

DRD

Total Cost 54,661,000.00 58,980,000.00 57,834,000.00 62,508,000.00

Unit Cost (R22,900/m) (R24,710/m) (R24,230/m) (R26,290/m)

NCD

Total Cost 14 169 000.00 15 237 000.00 14 964 000.00 16 124 000.00


ELB

Total Cost 11 633 000.00 12 433 000.00 12 187 000.00 13 062 000.00


The cost estimate for concrete and the reno-mattress lined alternatives are not far apart. However, the reno-

mattress lined canal has greater environmental advantages in terms of re-vegetation of the canal. The flow

velocities in the concrete lined canal will be higher and a disadvantage to the current ecosystem.

The cost to implement the 5 year recurrence interval design is marginally higher than the 2 year storm event.

However, the probability of overtopping is lower than the 2 year storm event. The cost should be looked at in the

entire context of the objectives of this project, and other related projects, and the downstream effects. For

instance, the volumes of impacted water (acid mine drainage) pumped and treated before discharge will be lower

in the 5 year design than the 2 year design. This will reduce the life-cycle cost considerably for acid mine

drainage treatment.

It is recommended that the reno-mattress option be taken to detailed design for the 5 year storm event.


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TABLE OF CONTENTS

SECTION PAGE

1 INTRODUCTION ...................................................................................................1

2 PROJECT LOCALITY .............................................................................................1

3 PROJECT MOTIVATION AND OBJECTIVE ................................................................1

4 PROJECT STAGES ...............................................................................................6

5 INCEPTION PHASE (SURVEYS AND INVESTIGATIONS) .............................................6

5.1 Topographical survey...................................................................................... 6 5.2 Geotechnical investigation ............................................................................... 6 5.3 Verification of areas of ingress .......................................................................... 7

6 CONCEPT AND VIABILITY STAGE (PRELIMINARY DESIGN) .......................................8

6.1 Basis of design .............................................................................................. 8 6.2 Catchment discretisation................................................................................ 10

6.2.1 DRD Site...................................................................................... 10 6.2.2 New Canada Dam Site .................................................................... 11 6.2.3 Elburgspruit Site ............................................................................ 12

6.3 Design approach and methodology .................................................................. 13 6.3.1 Rainfall determination ............................................................... 13 6.3.2 Runoff determination ................................................................. 13 6.3.3 Stormflow routing and canal sizing ............................................ 14 6.3.4 Effects of existing control structures .......................................... 14 6.3.5 Backwater analysis ................................................................... 15

6.4 Model input data .......................................................................................... 15 6.4.1 Rainfall data .............................................................................. 15 6.4.2 Catchment data ......................................................................... 16 6.4.3 Channel data ............................................................................. 19 6.4.4 Simulation data ......................................................................... 19

6.5 Hydrosim results................................................................................................................ 20 6.5.1 DRD Modelling results .............................................................. 20 6.5.2 NCD Modelling results .............................................................. 21 6.5.3 Elburgspruit Modelling results ................................................... 23

6.6 HEC-RAS Results ........................................................................................ 24 6.6.1 DRD Canal ................................................................................ 24 6.6.2 NCD Canal ................................................................................ 24 6.6.3 Elburgspruit Canal ..................................................................... 24

6.7 Earthworks design ....................................................................................... 24 6.8 Liner design ............................................................................................... 26 6.9 Entrance and exit design ............................................................................... 29 6.10 Safety aspects ............................................................................................ 29 6.11 Maintenance ............................................................................................... 29


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7 DESIGN PRINCIPLES AND CRITERIA ........................................................ 30

8 ENVIRONMENTAL REQUIREMENTS .................................................................... 30

9 OCCUPATIONAL HEALTH AND SAFETY REQUIREMENTS ...................................... 32

9.1 Design Stage – Risk Assessment .................................................................... 32 9.2 Prepare Health and Safety Specification ............................................................ 32 9.3 Evaluation and Approval of the Health and Safety Plan ......................................... 32

10 PROJECT IMPLEMENTATION PROGRAMME ......................................................... 33

11 PRELIMINARY COST ESTIMATE .......................................................................... 33

12 PROJECT RISKS ............................................................................................... 37

13 RECOMMENDATIONS AND CONCLUDING REMARKS ............................................ 38

LIST OF TABLES

Table 1: Design floods for different land uses ......................................................................................................... 9

Table 2: Raingauge data used in Hydrosim .......................................................................................................... 16

Table 3: DRD catchment characteristics ............................................................................................................... 16

Table 4: NCD catchment characteristics ............................................................................................................... 17

Table 5: Elburgspruit catchment characteristics.................................................................................................... 18

Table 6: Channel data used in Hydrosim .............................................................................................................. 19

Table 7: Design results for the DRD channel ........................................................................................................ 21

Table 8: Design results for the NCD channel ........................................................................................................ 22

Table 9: Design results for the Elburgspruit channel ............................................................................................. 24

Table 10: Liner design matrix scoring ................................................................................................................... 27

Table 11: Liner design decision making matrix ..................................................................................................... 27

Table 12: Preliminary cost estimate for the DRD Canal ........................................................................................ 34

Table 13: Preliminary cost estimate for the NCD Canal ........................................................................................ 35


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Table 14: Preliminary cost estimate for the Elburgspruit Canal ............................................................................ 36

Table 15: Summary of Cost Estimates .................................................................................................................. 37

LIST OF FIGURES

Figure 1: Study Area within the Witwatersrand Basin ............................................................................................. 2

Figure 2: Site Locality of DRD Canal ..................................................................................................................... 3

Figure 3: Site Locality of New Canada Dam Canal ................................................................................................. 4

Figure 4: Site Locality of Elburgspruit Canal ........................................................................................................... 5

Figure 5: Global Flow Probe ................................................................................................................................... 7

Figure 6: Flow measurement at the NCD site ......................................................................................................... 8

Figure 7: DRD Catchment Delineation .................................................................................................................. 10

Figure 8: DRD Canal at the R41 Road Crossing................................................................................................... 11

Figure 9: NCD Catchment Delineation .................................................................................................................. 12

Figure 10: Elburgspruit Catchment Delineation..................................................................................................... 13

Figure 11: DRD 2-year return period channel hydrograph .................................................................................... 20

Figure 12: DRD 5-year return period channel hydrograph .................................................................................... 21

Figure 13: NCD 2-year return period channel hydrograph .................................................................................... 22

Figure 14: NCD 5-year return period channel hydrograph .................................................................................... 22

Figure 15: Elburgspruit 2-year return period channel hydrograph ......................................................................... 23

Figure 16: Elburgspruit 5-year return period channel hydrograph ......................................................................... 23

Figure 17: Typical profile found at all sites ............................................................................................................ 25


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Figure 18: Organic material found at DRD Upstream ........................................................................................... 25

Figure 19: Weathered quartzite found at DRD and Elburgspruit ........................................................................... 25

Figure 20: Proposed liner with leak detection system ........................................................................................... 28

Figure 21: Proposed liner without leak detection system ...................................................................................... 28

LIST OF APPENDICES

Appendix A Preliminary Drawings

Appendix B Hydrosim Design Calculations

Appendix C Cost Estimate Breakdown

Appendix D Geotechnical Investigation Report

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1 INTRODUCTION

The Department of Mineral Resources (through the Council for Geoscience) intends implementing measures

for the prevention of water ingress into mined out areas in the Witwatersrand Goldfields. Three canals have

been identified, within natural watercourses, for lining along and across streams traversing shallow

undermined areas in the Witwatersrand Goldfields.

Zitholele Consulting was appointed to provide professional engineering services to the Council for

Geoscience (CGS) to undertake the design of the lining of these canals in order to render them significantly

impermeable to water ingress.

The canals identified under this project are:

Durban Roodepoort Deep (DRD) West Rand 2,400 metre section

New Canada Dam (NCD) Central 600 metre section

Elburgsrpuit (ELB) East Rand 590 metre section

2 PROJECT LOCALITY

Three sites were chosen by the CGS within the Witwatersrand mining basin as part of this project and are

shown on Figure 1. Each of the specific sites is shown in more details in Figure 2 to Figure 4.

3 PROJECT MOTIVATION AND OBJECTIVE

Ingress of surface water into underground mines, and the subsequent decant of the impacted water, is a

major concern in the Witwatersrand mining basin. The objective of this project is to alleviate the ingress of

surface water into underground mines in identified areas, by lining the canals to render them significantly

impermeable.

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Figure 1: Study Area within the Witwatersrand Basin

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Figure 2: Site Locality of DRD Canal

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Figure 3: Site Locality of New Canada Dam Canal

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Figure 4: Site Locality of Elburgspruit Canal

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4 PROJECT STAGES

The following stages typically make up the project life cycle.

The Inception stage is complete and was captured in the Project Implementation Report. The Project

Implementation Plan was approved by CGS before commencing with the Concept and Viability Phase. The

Inception/Implementation report dictates the scope of the project as well as the battery limits. This report

documents what has been undertaken during the Concept and Viability Phase.

5 INCEPTION PHASE (SURVEYS AND INVESTIGATIONS)

As a precursor to the Concept and Viability Stage, a topographical survey and geotechnical investigation

was initiated. It was also deemed necessary to confirm the areas of water ingress by undertaking a desktop

study as well as site measurements.

5.1 Topographical survey

Topographical surveys of the sites were carried out in July 2012. The results of these surveys were used in

the preliminary design of the canals and are reflected on the attached drawings. The survey is also

beneficial in identifying controls on the watercourse that may cause backwater effects if significant changes

are made to the river dynamics. For this reason, the lining material to the canal needs to be chosen

carefully taking into consideration its relative “roughness” and the subsequent canal flow velocities.

The natural profile along the river may vary intermittently within short sections of river lengths. However, for

construction practicalities, the design will vary the profile for significant changes in the slope only and not for

minor changes in slope. The overall river dynamics will remain intact.

5.2 Geotechnical investigation

A general authorisation from the Department of Water Affairs (DWA) was required to commence with the

geotechnical investigation as test pits were proposed to be excavated within the wetland. This was received

on the 20th December 2012. The geotechnical investigation was undertaken between the 16th and 18th

January 2012. A full geotechnical report will be made available towards the end of February 2013 as test

results of samples are awaited from the soils laboratory.

In summary, the sub-soils encountered within the sites are generally sandy and appear to be very loose to

loose in consistency and the majority of holes collapsed due to nature of the soils and a rapid ingress of

water into the pits. Clayey soils were also encountered but occasionally. These soils are mainly of alluvial

origin and some are disturbed due to the current artificial mining activities. Shallow rock at depths of

between 1,0 to 2,0 was encountered occasionally in some of the pits (DRD and Elburgspruit Canals). Heavy

machinery may be required if these depths need to be excavated.

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5.3 Verification of areas of ingress

A desktop study was undertaken using mining maps in order to verify the areas of water ingress. The

mining maps were superimposed on top of a 1:50,000 topographical map. Apart from the DRD site, the

rivers under consideration for the two other sites fall directly on top of undermined areas. As for the DRD

canal, a fault runs from the river to the under mined area which acts as a conduit for the conveyance of

water.

The second method to verify the loss of water along the river reaches under consideration was to do on site

flow measurements. This had to be undertaken during the rainy season. Each of the three sites was visited

shortly after storm events. Velocities in-stream was measured upstream and downstream of the river reach

under investigation. This was done using a Global Flow Probe.

Figure 5: Global Flow Probe

The apparatus is inserted into the stream at a third of its flow depth due to the parabolic velocity profile. An

instantaneous velocity is measured. The position where the flow measurement is taken as well as the flow

depth is recorded. Using the topographical survey of the sites, a cross sectional area of the position in the

river is delineated. The cross section area for the flow of water is then determined using the flow depth.

Using the following formula, the flow rate in m3/s is derived:

Q = V A

Where:

Q flow rate in m3/s

V flow velocity in m/s

A flow area in m2

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Figure 6: Flow measurement at the NCD site

After determining the flow rates, the following conclusions were reached:

The downstream flow at the DRD site is significantly lower than the upstream flow indicating that there

is evidence of infiltration into the underground mines;

The downstream flow at the NCD site is marginally lower that the upstream flow which could indicate

possible infiltration into the underground mines;

The downstream flow at the Elburgspruit site is higher than the upstream flow. This is due to discharge

from the adjacent mining activities between the upstream and downstream measurements. A

conclusive finding cannot be made here unless the discharge rate from the mines is known.

6 CONCEPT AND VIABILITY STAGE (PRELIMINARY DESIGN)

The project objective is to line the length of canal that traverses the defunct underground mines in order to

render them virtually impermeable. The new canals need to accommodate the 1 in 5 year storm interval

without overtopping. Smaller recurrence intervals storm events may be used which will result in smaller

designed canals (hence cheaper) but the probability of water ingress will be greater due to overtopping of

the canal more frequently.

6.1 Basis of design

The following factors were considered during the design of the canals for all three sites:

A general consideration to be made on all three sites is to ensure that there is insignificant impact on

upstream and downstream users on the watercourses that are proposed to be lined. The flow regime

within the watercourses should be maintained thereby sustaining aquatic life, post-development.

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It may not be economically feasible to line the wetlands to render it impermeable in certain areas due to

its vast surface area. The wetland delineation investigation and report will confirm the significance of

the wetland to flora and fuana.

The desktop study of previous reports indicates that a significant portion of the base flow in the

watercourses under consideration is due to illegal discharge of effluent. These amounts are not

quantified and the frequency of discharge is unknown. The only flow considered in the design is due to

stormwater runoff.

The Guideline for Human Settlement Planning and Design was used to determine the design flood in

the sizing of the canals. Table 6.2 from the guideline, as indicated in Table 1 below, shows the

appropriate recurrence interval to be used in the design. The design flood recurrence interval for a

general commercial and industrial land use was chosen as it is most appropriate to the sites under

consideration (i.e. a 5 year recurrence interval). However, the 1 in 2 year storm event will also be

considered for financial comparisons.

Table 1: Design floods for different land uses

LAND USE DESIGN FLOOD RECURRENCE

INTERVAL

Residential 1 – 5 years

Institutional (e.g. schools) 2 – 5 years

General commercial and industrial 5 years

High value central business districts 5 – 10 years

The Manning’s Roughness, “n”, of 0.022 was used for the reno mattress which is the industry norm.

This value is very critical as it determines the water depth in the canal.

A trapezoidal channel has been opted for with side slopes of 1 in 2. The shape offers more stability.

The longitudinal slope of the channel is as per the natural conditions. Minor changes made to the slope

will be for construction practicalities.

The only flow considered in the design of the canal is stormwater runoff from the delineated catchment

following the 1 in 2 and 5 year storm events. No illegal effluent discharges from industry will be

considered when designing the canals.

No modifications will be made to bridges crossing the watercourses under consideration. The

backwater effects of bridges will be taken into consideration in the design of the canals.

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6.2 Catchment discretisation

The three sites considered in this project are described in detail below.

6.2.1 DRD Site

The Durban Roodepoort Deep (DRD) site is located immediately to the west of Roodepoort. Zoning is

predominantly residential and industrial with past mining activities within the area. This includes tailings

dams. Apart from the buildings, most of the land is covered by open spaces and grasslands. Approximately

50 percent of the catchment area is impermeable which comprises of predominantly roof tops and paved

roads.

Figure 7: DRD Catchment Delineation

The water course under consideration is a tributary of the Klipspruit. Approximately 2.5 km of this

watercourse is proposed to be lined. This section runs in a south westerly direction and ends at the

confluence with the Klipspruit River.

The R41, Randfontein Road, runs across the bottom of the catchment. The watercourse crosses under the

road at the culvert as shown on

Figure 8 below.

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Figure 8: DRD Canal at the R41 Road Crossing

The culvert is approximately 7 metres wide by 2 metres high. The design will need to determine whether the

culvert is adequately sized to convey the design flow and the possible backwater effects of the culvert (if

any).

There are a few water bodies within the catchment which could offer attenuation of flow during storm events.

Due to the sizes of these structures compared to the catchment and their operation (operating levels), it is

prudent to ignore these attenuation effects during design.

6.2.2 New Canada Dam Site

The New Canada Dam (NCD) site is located in Johannesburg South, between the areas of Stormill and

Wibsey Dip. A significant portion of the river reach under consideration runs adjacent, to the east, to an

existing gold tailings dam before it crosses under Main Reef Road (R41) via a major road bridge. The lining

to the river reach will terminate just south of Main Reef Road, between the Stormill and Pennyville industrial

areas.

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Figure 9: NCD Catchment Delineation

The northern portion of the river is quite close to the tailings dam, approximately 40 metres away. A major

concern is the washout of material from the tailings dam into the channel. However, this will be mitigated

against by the implementation of cut-off berms in this area.

The catchment that drains to this river reach comprises mainly of residential areas. There are also non-

functional mines with their tailings dams that fall within the catchment. A few industrial areas are located

within the catchment. There is no noticeable larges area of grassland which makes this catchment

impermeable hence increasing the run-off.

Apart from paddocks that serve the tailings dam which is located adjacent to the river reach, there are no

dams within the river reach.

6.2.3 Elburgspruit Site

The area under consideration is the river reach that runs along Knights Mining located approximately 4

kilometres north-east of Germiston central business district. The river reach runs from Knights Mining in a

southern direction over the Main Reef before it crosses under Main Reef Road (R29) via a 1 metre diameter

pipe culvert. The river terminates as a natural stream at a manmade dam approximately 500 metres south of

Main Reef Road. The water is then conveyed across the Bird Reef via a 700mm diameter concrete pipe.

The catchment draining to this portion of river comprises mainly of residential areas with a significant

number of industrial areas towards to north of the catchment. Evidence of previous mining activities is

located to the southern portion of the catchment.

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Figure 10: Elburgspruit Catchment Delineation

6.3 Design approach and methodology

The three sites were modelled separately using Hydrosim (Version 5.2), a rainfall-runoff model used in the

determination of storm flows and stormwater infrastructure sizing. The following inputs are required by the

model to generate specific rainfall events and subsequent storm flows.

6.3.1 Rainfall determination

Mean Annual Precipitation (MAP) of the catchment under consideration. The model is equipped with a

database of rainfall gauges within Southern Africa and information for the rainfall gauge closest to the

site may be selected.

An Aerial Reduction Factor (ARF) needs to be given which is dependent on the size of the catchment;

Rainfall distribution – this could either be rectangular (constant intensity throughout the storm duration)

or triangular (intensity peaks a third into the storm duration). A triangular rainfall distribution was chosen

as this best describes the rainfall event;

The location of the catchment needs to be given as coastal or inland in order to utilise the correct

algorithm for storm generation

6.3.2 Runoff determination

The next step is to define the catchments and populate the model with the catchment characteristics.

Information required includes the following:

Size of catchment

Average slope along the catchment towards the lowest point (natural watercourse)

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Distance from the watershed to the watercourse (generally termed the overland flow length)

Land cover of the catchment. This will generally be divided in the areas that are impermeable (roof

tops, paved areas, etc.) and permeable (veld areas). The intention is to determine the rate of infiltration

(recharge as groundwater) and the percentage of rain that is actually converted to stormflow (runoff).

6.3.3 Stormflow routing and canal sizing

The storm flow is generated from the catchment using the information given above and will be routed to the

canal. However, the canal will need to be sized for the specific storm event based on the following input

criteria:

Length of canal,

Longitudinal slope;

Side slopes;

Manning’s roughness, “n”, based on the material of construction;

Base width

The canal will be sized using the information given above for various recurrence interval storm events.

6.3.4 Effects of existing control structures

In most instances there will exist, along the watercourse, control structures. These may include:

Dams;

Weirs;

Culverts or bridges

Although the canals may be adequately sized for a specific storm event, the control structures may cause

overtopping of the canals upstream of them. This is due to the backwater effects that the control structures

may have as they themselves have not been adequately sized for that specific storm event.

In order to check for the adequacy of existing control structures to convey the relevant flows without

attenuation and significant backwater effects, the HEC-RAS backwater model was used.

It is not the intention or scope of this project to make significant modifications to road crossings as this

infrastructure falls under the remit of other custodians, namely the road authorities. If this infrastructure does

cause significant backwater effects, the canal will be sized accordingly to ensure that the floodline is

contained within it. This is discussed further in the subsequent section.

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6.3.5 Backwater analysis

As mentioned previously, the HEC-RAS backwater model will be utilised to check for significant backwater

effects caused by existing culverts within the watercourses under consideration. The model utilises

numerous hydraulic formulae in its assessment and produces a floodline based on the given flows

(generated from Hydrosim). The floodline will indicate if the flow is contained within the proposed canal and

where modifications are required in order to accomplish this.

Cross sections of the watercourses under consideration must be input to the model. Information gathered

from the topographical survey of the sites were utilised in determining the cross-sections of the relevant

watercourses. However, the proposed designed canal should be used as part of the cross-section to

simulate the post development conditions.

6.4 Model input data

Various input data is required for the catchments under consideration in order to determine the flow rates for

the various return periods. These are given below.

6.4.1 Rainfall data

Hydrosim has a built-in database pre-populated with rainfall data for the entire country. The rain gauge for

the weather station closest to the site was used in each case in order to determine the design storm event.

Apart from the Mean Annual Precipitation (MAP) of the relevant rain gauge, other important factors influence

the rainfall intensity and duration. The following variables are common with the three sites:

Region Inland

Storm type Triangular

Areal reduction factor As per the model based on the size of catchment

Time to peak one third of the storm duration

Specific information for each site is given in Table 2 below.

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Table 2: Raingauge data used in Hydrosim

Site Name Raingauge

location

WB No. Altitude

(mamsl)

MAP (mm)

DRD Roodepoort

Municipality

0475669W 1,780 737

NCD Clydesdale

Colliery

0438744W 1,465 622

Elburgspruit Germiston – FJ

Payne Park

0476283W 1,663 729

6.4.2 Catchment data

Apart from the size of the catchment and its developed portion, many other factors influence how much of

the rainfall generated above is converted to surface flow that contributes to flow in the receiving water

courses. The topography of the land, especially the catchment gradient, as well as the sub-soils has a

significant influence in the percentage of run-off generated in the catchment.

The catchment characteristics identified for the DRD catchment and used in the model is given in the table

below.

Table 3: DRD catchment characteristics

Description Value Unit

Catchment area 2,386 ha

Overland flow length 2,173 m

Slope 0.037 m/m

Percentage impervious area 50 %

Overland Manning’s factor

for pervious fraction

0.200 unitless


for impervious fraction

0.016 unitless

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*Depression storage for

pervious fraction

4.0 mm


impervious fraction

1.5 mm

**Initial infiltration rate 45.0 mm/hr

**Final infiltration rate 6.0 mm/hr

*Dependant on the slope **Dependant on sub-soil conditions

The catchment characteristics identified for the NCD catchment and used in the model is given in the table

below.

Table 4: NCD catchment characteristics




Slope 0.050 m/m




0.200 unitless



0.016 unitless


pervious fraction

4.0 mm


impervious fraction

1.5 mm



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The catchment characteristics identified for the Elburgspruit catchment and used in the model is given in the

table below.

Table 5: Elburgspruit catchment characteristics




Slope 0.050 m/m




0.200 unitless



0.016 unitless


pervious fraction

4.0 mm


impervious fraction

1.5 mm



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6.4.3 Channel data

The information input to the model allows for an “auto design” of the channel. This simply means that the

flow depth in the channel is designed during simulation of the different storm events. Only a minimum depth

is input to the model. In all cases this was 100mm.

A trapezoidal channel was opted for due to the following reasons:

Minimum velocities are maintained at low flows;

Easily constructed;

Sides more stable without additional reinforcing;

Safer than vertical side walls

The side slopes of the trapezoidal channels were same for all three sites, 1 vertical to 2 horizontal. The

widths of the bases differed for the site and are represented in the respective tables below. Initially a base

width of 5 meters was opted for but this resulted in significantly deeper channels on some of the sites and

consequently resulted in berms being constructed on either side of the channels. This is not the ideal case

as it prevents surface run-off from entering the channel. A 10 metre base width was then chosen and

resulted in a more practical solution.

Manning’s roughness coefficient in the channel took into consideration the proposed materials to be used in

the liner design. The roughness coefficient of 0.022 for reno-mattress was used as this comes in direct

contact with the streamflow.

The channel data input to the model is given in Table 6 below.

Table 6: Channel data used in Hydrosim

Site Name Length (m) Slope (m/m) Base width(m)

DRD 2,387 0.008 10

NCD 600 0.006 10

Elburgspruit 590 0.020 5

6.4.4 Simulation data

It was agreed, amongst the project team, that the canals should be sized for both the 2 and 5 year storm

events during the preliminary design stage. Once the cost estimates are determined for both scenarios and

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the risks identified with a shorter return period, a joint decision will be made on which option to take forward

to detailed design.

A storm duration is required as input to the model in order to generate the storm flow. This is dependent on

the size of the catchments and the lag within the catchment. A storm duration of an hour was chosen for all

three sites as the peak flows should occur during this period. This was confirmed running the model for

shorter and longer storm durations.

6.5 Hydrosim results

The ultimate objective of the model is to determine the depth of flow in the channels for the different return

periods modelled. Other output data generated from the model is used as a check for the accuracy of the

model and to alert the user for any anomalies in the results. One of the most significant outputs for

verification is the hydrographs. There needs to be a lag between the inflow and the outflow from the channel

and the total volumes under the curve should be the same.

The model results for each of the sites are described below.

6.5.1 DRD Modelling results

The channel hydrographs for each design storm scenario is shown for the DRD site in the figures below.

Figure 11: DRD 2-year return period channel hydrograph

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Figure 12: DRD 5-year return period channel hydrograph

The corresponding design heights of the channels for the above hydrographs are given in Table 7 below.

Table 7: Design results for the DRD channel

Recurrence

Period

Flow (m3/s) Design height (mm) Velocity (m/s)

2 94 1,560 3.89

5 144 2,000 4.37

The design indicated in the table above excludes a minimum freeboard of 300mm.

6.5.2 NCD Modelling results

The channel hydrographs for each design storm scenario is shown for the NCD site in the figures below.

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Figure 13: NCD 2-year return period channel hydrograph

Figure 14: NCD 5-year return period channel hydrograph


Table 8: Design results for the NCD channel

Recurrence

Period


2 81 1,550 3.22

5 120 2,000 3.31


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6.5.3 Elburgspruit Modelling results

The channel hydrographs for each design storm scenario is shown for the Elburgspruit site in the figures

below.

Figure 15: Elburgspruit 2-year return period channel hydrograph

Figure 16: Elburgspruit 5-year return period channel hydrograph


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Table 9: Design results for the Elburgspruit channel

Recurrence

Period


2 81 1,523 4.78

5 118 1,900 4.89


6.6 HEC-RAS Results

A preliminary design of the ability of the existing culverts located at the three sites was undertaken using

HEC-RAS, a backwater model. The results of the model are as follows:

6.6.1 DRD Canal

A box culvert, 7metres wide by 1.84 metres high, exists at the Randfontein road crossing located at the

upper reach of the river. The preliminary design indicates that the culvert is adequately sized to take the 2

year storm event but fails to convey the 5 year storm event without having a significant backwater effect.

The culvert will need to be upgraded if the 5 year storm event is chosen as our design flood event.

6.6.2 NCD Canal

The road crossing located at Main Reef Road where the canal crosses is adequately sized to convey flows

in excess of the 5 year storm event and should not pose a problem.

6.6.3 Elburgspruit Canal

The culvert located at the end of the reach under consideration comprises of a 1 metre diameter pipe which

is not adequately sized to convey the 2 year storm event. Once the design flood is finalised, this culvert will

be sized accordingly.

6.7 Earthworks design

A geotechnical investigation was carried out and is described briefly under Section 5.2 of this report. A

comprehensive geotechnical investigation report is attached to the appendices. The results of this

investigation form the basis of the earthworks design.

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Figure 17: Typical profile found at all sites

Figure 18: Organic material found at DRD Upstream

Figure 19: Weathered quartzite found at DRD and Elburgspruit

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Figure 17 displays a typical test pit encountered on all three sites. Apart from a few areas where weathered

quartzite was encountered at levels between 1.5 and 2 metres as shown in Figure 19, a pioneer layer of

dump rock will be required in these areas in order to create a viable working surface. The dump rock will be

compacted in 500mm layers typically and compacted using approximately 9 passes of a heavy vibratory

roller. Some organic material was found at the DRD site at the upstream end located within a wetland. This

is shown in Figure 18.

6.8 Liner design

The choice of liner is fundamental to the objectives of this project and should adhere to the following

conditions:

It must be impermeable to the ingress of water;

Maintain the current in stream velocities;

Adequate availability of material in close proximity to the sites;

Environmentally friendly liner which facilitates re-vegetation within the channel;

Economically viable;

Aesthetically pleasing;

Flexible enough to accommodate slight deflections

Safety – ability to exit the canal by foot

The following possible alternatives were considered for the liner design:

Concrete;

Rip-rap or stone pitching;

Grass blocks;

Hyson cells;

Pipelines (HDPE or concrete pipes with spigot and sockets joints)

Reno-mattress

Apart from the pipeline alternative, all the other options were considered in conjunction with a HDPE backing

layer.

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The matrix below summarises the reason for using the reno-mattress as the preferred option for the liner

design. A score was given for each of the alternative with regards to compliance with the conditions as

mentioned above. The scoring as indicated in Table 10 below.

Table 10: Liner design matrix scoring

Table 11: Liner design decision making matrix

Cost Environ Aesthetic Flexibility Safety Velocity Total

Concrete 3 1 2 1 1 1 9

Stone

pitching 4 1 3 1 2 3 14

Grass

blocks 4 2 3 3 2 3 17

Hyson

cells 3 1 2 1 1 1 9

Pipelines 1 3 3 3 5 1 16

Reno-

mattress 3 5 5 5 3 5 26

1 Unsatisfactory

2 Fair

3 Satisfactory

4 Good

5 Excellent

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The scores in the table above describe the ability of each alternative against the condition set.

The liner design using reno-mattress will only be considered as it is deemed to be the most viable option.

There are two types of liners that may be considered. One is with a leak detection system and the other is

without. These are portrayed in the sketches below

Figure 20: Proposed liner with leak detection system

Figure 21: Proposed liner without leak detection system

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The leak detection system will be connected to a series of manholes that is filled with water if the HDPE liner

is compromised by sharp objects that could lodge in between the reno-mattress. The manholes will be left

to accumulate water and is monitored by the maintenance staff if leaks occur. However, the anticipated

volumes of water will not be significant following a small puncture in the HDPE geomembrane and may not

warrant the installation of a leak detection system. This needs to be addressed under the Risk component

of the project.

The other components of the liner system, excluding the leak detection system, are as follows (from bottom

to top of liner):

Grade A4 bidim on top of dump rock pioneer layer;

19mm crushed stone wrapped in bidim – this acts as conduit to relieve upward pressure from

groundwater that may deform the HDPE geomembrane;

1.5mm HDPE geomembrane;

Grade A6-8 bidim – this serves as a cushion layer between the HDPE geomembrane and the reno-

mattress and prevents puncturing of the geomembrane;

300mm thick reno-mattress secured to gabion baskets along its length.

6.9 Entrance and exit design

In order to prevent scouring behind the liner at the entrance and exit to the channel, headwalls are proposed

at these two locations. The headwalls is proposed to be constructed from reinforced concrete and may have

stone pitched facing in order to blend in with the environment.

Apart from erosion control, the liner system will be anchored to the headwalls to ensure stability along its

length.

6.10 Safety aspects

It is proposed that both sides of the entire length of the channel be fenced off with a 2.4 metre high concrete

palisade with vehicular access gates at both ends as per the client’s requirements.

Lifesaving flotation devices will be installed at 200 metre intervals along the length of the canal.

6.11 Maintenance

A vehicle access road will be constructed along one side of the canal. This will accommodate a small

vehicle used to clean the canal of any debris that is lodged in the reno-mattress.

A pedestrian bridge will be constructed at the centre of the shorter canals and at every 500 metres at the

DRD canal. This will basically be a galvanised mild steel bridge with handrails supported on reinforced

concrete abutments on either side.

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7 DESIGN PRINCIPLES AND CRITERIA

The following design principles and criteria will be adopted in the design and implementation of the proposed

works:

SANS 1200 will be used for the civil engineering specifications for the works. Additions and variations

to this will be clearly stated

General Conditions of Contract (Second Edition, 2010) will be used as the conditions of contract for the

construction works

A 1.5mm HDPE sheet will be used as the impermeable layer in the canal liner and will be subject to

destructive testing during construction;

The walls of the entrance and exit structures will be constructed from 35 MPa concrete with high yield

stress reinforcing bars. Bar diameters will be confirmed at detailed design stage

A smooth finish (Clause 5.2.1(b), SANS 1200G) will be required on the walls of the new entrance and

exit structures

The reno-mattress will be manufactured from galvanised wires and filled with selected stone and

carefully finished

All fill material to be imported from approved commercial sources

The project will need to be undertaken during the winter periods i.e. during low flow conditions.

8 ENVIRONMENTAL REQUIREMENTS

In terms of the National Environmental Management Act, (Act No 107 of 1998) and Government Notice

R.544, the lining of the three separate canals triggers an Environmental Authorisation. Zitholele approached

the Department of Environmental Affairs (DEA) and an agreement was reached which stated that should the

applicant be able to secure a licensed re-processing facility/dump to accept the excavated materials, only a

Basic Assessment would be required. The main process of the Basic Assessment comprises the following:

Application form: An application to undertake a BA process together with the Environmental

Assessment Practitioner (EAP) declaration of independence has been submitted to the DEA to obtain a

reference number and for the DEA to assign a case officer to the project.

Desktop studies and terrain evaluation: The study area will initially be studied through desktop

studies. This will give the environmental practitioner the opportunity to evaluate the study area and to

identify any critical and obvious fatally flawed areas within the study area. The consultant will identify

any potential issues with the refurbishment activities, and indicate critical findings to the client.

Orthophotos and topographical maps as well as internet searches will be used during the desktop study

and desktop terrain evaluation.

Identification of stakeholders and development of a register of Interested and Affected Parties

(I&APs): Stakeholders’ details will be captured on Maximiser 9, an electronic database management

software programme that automatically categorises all mailing to stakeholders, thus providing an

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ongoing record of communications. Stakeholders will be identified according to the criteria specified in

the NEMA regulations (under Section 24(5) of the NEMA);

Announcement of the proposed project and opportunity to comment: The project will be

announced through the distribution of a Background Information Document (BID) (inclusive of a reply

and registration sheet), placement of advertisements in local/regional media and placement of site

notice boards. The Zitholele website will be used for the publishing of all public documents such as the

BID, adverts and site notices;

Specialist Studies: The specialist studies proposed to be undertaken for the project, as per the Scope

of Works, include Terrestrial Ecology in Avi-faunal, Visual, Surface Water / Wetland Delineation, GIS,

Heritage Assessment as well as a Water use License Application. It should be noted that these

specialist studies represent identified studies from a potential list of studies. As the site is currently

unknown from a specialist’s point of view, the characteristics of the site will have to be confirmed, along

with the list of specialist studies, once the site has been visited. Therefore these studies are merely an

indication of the potential studies that could be required.

Impact assessment and terrain evaluation: The BA Report will include the activity description; site

descriptions; public participation; a description of the issues and assessment of the alternatives. The

specialist studies results will be summarised and integrated into the BA Report.

Environmental Management Programme: An EMP, in the context of the Regulations, is a tool that

takes a project from a high level consideration of issues down to detailed workable mitigation measures

that can be implemented in a cohesive and controlled manner. The objectives of an EMP are to

minimise disturbance to the environment, present mitigation measures for identified impacts, maximise

potential environmental benefits, assign responsibility for actions to ensure that the pre-determined aims

are met, and to act as a “cradle to grave” document. An EMP will be drafted according to the findings in

the BAR. The EMP will be prepared taking cognisance of any existing EMP’s for infrastructure in the

study area and assessed impacts.

Compilation of an Issues and Responses Report which will be updated throughout the duration of the

project;

Announcement of the availability and public review of the Draft Basic Assessment Report and its

associated Draft Environmental Management Plan: A period of four weeks will be allowed for public

comment. The availability of the report will be announced by way of personal letters to stakeholders and

an advertisement. The draft report will be made available at public places, sent to stakeholders

requesting a copy and also published on the Zitholele web site;

Announcement of the submission and availability of the Final Basic Assessment Report and its

associated Final (dynamic) Environmental Management Plan: A letter will be distributed to stakeholders

announcing the submission of the reports to the DEA and the availability to the final report on request;

Announcement of Environmental Authorisation: A letter will be faxed, emailed and mailed to

stakeholders announcing the environmental authorisation and the process for appeals.

The separate projects also require a Water Use License Application (WULA) to be lodged to the Department

of Water Affairs (DWA). During the meeting held at CGS on Thursday 14 February 2013, the client indicated

that they will handle the WULA with DWA.

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9 OCCUPATIONAL HEALTH AND SAFETY REQUIREMENTS

The OHS Agent function forms part of our scope of work but is limited to preparing the specifications. An

independent sub-consultant should be appointed to undertake the monitoring aspect of the project.

In terms of Regulation 4 as reflected in the Construction Regulations (2003):

4(5) A Client may appoint an Agent in writing to act as his/her representative and where such an

appointment is made, the responsibilities as imposed by these regulations upon a client shall, as far as

reasonable practical, apply to the Agent.

The Safety Agent is responsible to ensure that the Principal Contractor appointed by the Client adhere to the

Occupational Health and Safety Act (Act 85 of 1993) and the attendant regulations.

The scope of the Safety Agent shall include the following Occupational Health and Safety (OHS) functions

up to and including tender stage.

9.1 Design Stage – Risk Assessment

A site visit was undertaken to conduct a risk assessment (based on probability, severity and frequency)

during the design stage to identify hazards and recommend suitable mitigation measures to render the

project safe. Risks will be incorporated in the Health and Safety Specifications.

9.2 Prepare Health and Safety Specification

A Health and safety Specification will be prepared for the construction work to be performed. The

Specification will allow the Contractor to consider the necessary health and safety requirements pertaining to

the construction works so as to ensure health and safety of affected persons.

The Health and Safety Specifications aims to Discharge the Council’s responsibilities in terms of the

Occupational Health and safety Act (Act 85 of 1993) and the attendant regulations. The most noteworthy of

these regulations are the Construction Regulations (2003), the General Administrative Regulations (2003)

and the General Safety Regulations (1986 and subsequent amendments).

9.3 Evaluation and Approval of the Health and Safety Plan

The Health and Safety Plan of the Principal Contractor shall be reviewed in terms of the Health and Safety

Specification. Particular emphasis will be placed on the Risk Assessment and the concomitant Safe Work

procedures, OHS related responsibilities, cost provisions and general OHS provisions to comply with

statutory requirements.

The Review of the Health and Safety Plan will be undertaken by completing a detailed checklist and

comments sheets, which will be distributed to the relevant parties. All requisite amendments to the Health

and Safety Plan will be facilitated. The final Health and Safety Plan will be approved in writing.

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10 PROJECT IMPLEMENTATION PROGRAMME

A summary of the current status of each phase of the project follows (please refer to the Project Programme

attached to the appendices for the detailed implementation programme):

PHASE STATUS AND COMMENTS

Planning

Formalise project team Complete

Desktop study Complete

Investigations

Topographical survey Complete

Geotechnical Complete

Environmental Basic Assessment Report to be submitted

Preliminary Design Phase

Preliminary Design Report Draft complete (this report)

Approval (CGS) Awaiting

Detailed Design and Tender Phase

Detailed Design To commence on approval of PDR – projected

mid April 2013

Tender and Appointment Projected end July 2013

Construction and Monitoring Phase

Construction and monitoring Phase Projected start August 2013 for 12 months

Project Close-out Phase

Project Close-out Projected July 2014

Project end date Projected July 2014

11 PRELIMINARY COST ESTIMATE

The cost estimate was undertaken for the 2 year and 5 year recurrence intervals. A comprehensive cost

breakdown was done for the design which makes use of reno-mattresses. In order to draw a direct

comparison with other alternatives, a cost for the concrete lined option was undertaken. The cost

breakdown is attached to the appendices. An alternative using HDPE or concrete pipes will not be

economically viable as the unit rates are significantly higher than that of concrete or reno-mattresses.

A summary of the costs for each of the sites are summarised in the tables below for the two options

considered.

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Table 12: Preliminary cost estimate for the DRD Canal



Site clearance 542,804 584,815 542,804 584,815

Earthworks 14,760,676 16,027,354 14,760,676 16,027,353

Sub-liner system 9,487,916 10,544,740 9,487,916 10,544,740

Structural work

(headwalls and

bridges)

1,320,000 1,320,000 1,320,000 1,320,000

Fencing 4,631,040 4,631,040 4,631,040 4,631,040

Roads 2,088,625 2,088,625 2,088,625 2,088,625

Liner 6,922,605 7,697,610 9,230,141 10,263,479

Sub-total 1 39,753,665 42,894,183 42,061,201 45,460,052

P&G Items at 25% 9,938,416 10,723,546 10,515,301 11,365,013

Sub-total 2 49,692,082 53,617,729 52,576,501 56,825,065

Contingencies at

10% 4,969,208 5,361,773 5,257,651 5,682,507

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Total Cost

Estimate 54,661,290 58,979,501 57,834,151 62,507,572

Table 13: Preliminary cost estimate for the NCD Canal



Site clearance 136 200.00 147 000.00 136 200.00 147 000.00

Earthworks 3 692 887.18 4 017 966.16 3 692 887.18 4 017 966.16

Sub-liner system 2 414 794.45 2 656 476.71 2 414 794.45 2 656 476.71

Structural work

(headwalls and

bridges)

600 000.00 600 000.00 600 000.00 600 000.00

Fencing 1 200 000.00 1 200 000.00 1 200 000.00 1 200 000.00

Roads 525 000.00 525 000.00 525 000.00 525 000.00

Liner 1 735 649.26 1 934 882.92 2 314 199.02 2 579 843.89

Sub-total 1 10 304 530.89 11 081 325.78 10 883 080.64 11 726 286.76

P&G Items at 25% 2 576 132.72 2 770 331.45 2 720 770.16 2 931 571.69

Sub-total 2 12 880 663.61 13 851 657.23 13 603 850.80 14 657 858.45

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Contingencies at

10% 1 288 066.36 1 385 165.72 1 360 385.08 1 465 785.84

Total Cost

Estimate 14 168 729.97 15 236 822.95 14 964 235.88 16 123 644.29

Table 14: Preliminary cost estimate for the Elburgspruit Canal



Site clearance 103 792.80 112 690.00 103 792.80 112 690.00

Earthworks 3 155 732.89 3 370 875.53 3 155 732.89 3 370 875.53

Sub-liner system 1 695 568.62 1 889 384.49 1 695 568.62 1 889 384.49

Structural work

(headwalls and

bridges) 600 000.00 600 000.00 600 000.00 600 000.00

Fencing 1 180 800.00 1 180 800.00 1 180 800.00 1 180 800.00

Roads 516 250.00 516 250.00 516 250.00 516 250.00

Liner 1 208 216.99 1 372 348.63 1 610 955.99 1 829 798.17

Sub-total 1 8 460 361.30 9 042 348.65 8 863 100.30 9 499 798.19

P&G Items at 25% 2 115 090.33 2 260 587.16 2 215 775.07 2 374 949.55

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Sub-total 2 10 575 451.63 11 302 935.81 11 078 875.37 11 874 747.74

Contingencies at

10% 1 057 545.16 1 130 293.58 1 107 887.54 1 187 474.77

Total Cost

Estimate 11 632 996.79 12 433 229.39 12 186 762.91 13 062 222.51

Table 15: Summary of Cost Estimates



DRD 54,661,290.04

(R22,900/m)

58,979,500.85

(R24,710/m)

57,834,150.69

(R24,230/m)

62,507,571.74

(R26,290/m)

NCD 14 168 729.97

(R23,615/m)

15 236 822.95

(R25,400/m)

14 964 235.88

(R24,940/m)

16 123 644.29

(R26,870/m)

Elburgspruit 11 632 996.79

(R19,720/m)

12 433 229.39

(R21,070/m)

12 186 762.91

(R20,655/m)

13 062 222.51

(R22,140/m)

12 PROJECT RISKS

The following risks identified at preliminary design phase need to be addressed before proceeding with detail

design:

The design flow should comply with the Guidelines for Human Settlement as described earlier in the

report. However, the cost of implementation is also a factor that would influence which design flow is

chosen. One of the key stakeholders that may influence this decision is the Department of Water Affairs

(DWA). They should be consulted prior to engaging in detailed design.

Some of the existing culverts are not sized to convey even the 2 year storm event. These culverts need

to be expanded in order to convey the design flow. Discussions are required with the appropriate

authorities in order to increase the capacity of the culverts. Prior to this happening, the design flows to

be adopted need to be confirmed.

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One of the assumptions that were made during initial consultation with the Department of Environmental

Affairs (DEA) is that the spoil material disposed off-site shall be spoilt to a licensed facility. The CGS

need to acquire permission from a licensed facility to accept this material and notification in writing

should be submitted to the DEA. If this is unattainable, then a full Environmental Impact Assessment

will be required.

It is the opinion of the consulting team that a Water Use Licence (WUL) is required for construction.

This has not been initiated as yet and may delay both the issue of an Environmental Authorisation and

ultimately the project.

All specialist studies that are required for this project must be initiated within the rainy season. If these

specialist studies are not completed by the end of April, we may need to wait until September to do

them. This may delay construction.

The design flows excludes additional illegal discharge into the canal.

13 RECOMMENDATIONS AND CONCLUDING REMARKS

The cost estimate for concrete and the reno-mattress lined alternatives are not far apart. However, the reno-

mattress lined canal has greater environmental advantages in terms of re-vegetation of the canal. The flow

velocities in the concrete lined canal will be higher and a disadvantage to the current ecosystem.

The cost to implement the 5 year recurrence interval design is marginally higher than the 2 year storm event.

However, the probability of overtopping is lower than the 2 year storm event. The cost should be looked at

in the entire context of the objectives of this project and the downstream effects. For instance, the volumes

of impacted water (acid mine drainage) pumped and treated before discharge will be lower in the 5 year

design than the 2 year design.

It is recommended that the reno-mattress option be taken to detailed design for the 5 year storm event.

Approval from the CGS is required before engaging with detailed design.

N Rajasakran PrEng S Pillay PrEng

for Zitholele Consulting (Pty) Ltd

Documents

APPENDIX D1.1: Preliminary Design Report - zitholele - BA for 3 Canals/3. Final Basic... · APPENDIX D1.1: Preliminary Design Report. ... summarised in the table below. ... 6.1 Basis